Biological Psychology: Movement

KEY TERMS

Module 7.1

• Aerobic: Referring to processes that require oxygen.

• Anaerobic: Relating to processes that do not require oxygen.

• Antagonistic: Pertaining to muscles that work against each other to produce movement.

• Muscles: Tissues in the body that can contract to produce movement.

• Ballistic: A type of movement that is quick and powerful, often involving a fast release of energy.

• Movement: The act or process of changing position or location.

• Cardiac muscles: Muscles that make up the heart, responsible for pumping blood.

• Central pattern generators: Network of neurons that manage rhythmic movements, such as walking.

• Extensor: Muscle that extends or straightens a limb.

• Golgi tendon organs: Sensory receptors that detect tension in muscles.

• Flexor: Muscle that bends or decreases the angle between body parts.

• Fast-twitch fibers: Muscle fibers that contract quickly and are used for short bursts of speed.

• Motor program: A set of commands sent from the brain to execute a movement.

• Muscle spindle: A sensory receptor located in muscles that detects changes in muscle length.

• Neuromuscular junction: The synapse or connection between a motor neuron and a muscle fiber.

• Proprioceptor: Sensory receptor that receives stimuli from within the body, mainly related to position and movement.

• Reflexes: Automatic responses to stimuli.

• Skeletal (striated) muscles: Muscles attached to bones that facilitate movement.

• Slow-twitch fibers: Muscle fibers that are more fatigue-resistant and used for endurance activities.

• Smooth muscles: Involuntary muscles found in organs that are not under conscious control.

• Stretch reflex: An automatic muscular response to being stretched.

Module 7.2

• antisaccade task: A task that measures the ability to inhibit a reflexive eye movement in response to a stimulus.

• basal ganglia: A group of nuclei in the brain involved in coordinating movement and cognitive processes.

• cerebellar nuclei: Clusters of neurons located in the cerebellum that play a key role in the coordination of movement.

• corticospinal tracts: Neural pathways that transmit signals from the cerebral cortex to the spinal cord, controlling voluntary movements.

• lateral corticospinal tract: The major pathway for voluntary motor control, primarily responsible for fine motor skills in limbs.

• medial corticospinal tract: A pathway involved in controlling postural and trunk movements.

• mirror neurons: Neurons that fire when an individual observes an action performed by another, thought to be involved in understanding intentions and social interactions.

• parallel fibers: Axons that run parallel to each other in the cerebellum, playing a crucial role in cerebellar processing.

• posterior parietal cortex: A part of the brain that integrates sensory information and helps in spatial awareness and movement planning.

• prefrontal cortex: The region of the frontal lobe associated with complex cognitive behavior, decision making, and moderating social behavior.

• premotor cortex: An area of the brain responsible for planning and coordinating movements before they are executed.

• primary motor cortex: The section of the brain that directly controls voluntary movements of skeletal muscles.

• Purkinje cells: GABAergic neurons found in the cerebellum, which act to inhibit and modulate the activity of other neurons within cerebellar circuits.

• readiness potential: A measure of brain activity that precedes voluntary movement, indicating preparation for action.

• red nucleus: A structure in the midbrain involved in motor coordination and the control of limb movements.

• striatum or dorsal striatum: A component of the basal ganglia involved in the regulation of movement and a variety of cognitive functions.

• supplementary motor cortex: An area of the brain involved in the planning of movements and coordination of complex movements.

Module 7.3

• huntingtin: A protein that is produced by the HTT gene, mutations in which cause Huntington's disease.

• Huntington's disease: A genetic disorder characterized by the degeneration of neurons in certain areas of the brain, leading to motor dysfunction, cognitive decline, and psychiatric symptoms.

• L-dopa: A medication used to treat Parkinson's disease, it is a precursor to dopamine that helps improve motor symptoms by replenishing dopamine levels in the brain.

• MPP+: A neurotoxin derived from MPTP that selectively damages dopaminergic neurons and is used in research to model Parkinson's disease in animals.

• MPTP: A synthetic compound that causes Parkinson-like symptoms by inducing the degeneration of dopaminergic neurons in the substantia nigra when metabolized into MPP+.

• Parkinson's disease: A neurodegenerative disorder that primarily affects movement, causing tremors, rigidity, and bradykinesia due to the loss of dopamine-producing neurons.

• stem cells: Undifferentiated cells that have the potential to develop into various cell types, including neurons, and are being researched for their potential to treat neurodegenerative diseases like Parkinson's and Huntington's disease.

NOTES

Chapter 7

7.1 The Control of Movement

• The brain is fundamentally linked to the concept of movement, essential for actions and reactions to environmental stimuli. Internal processing necessitates the ability to move.

Muscles and Their Movements

• All animal movement relies on muscle contractions which fall into different categories:
    - Smooth muscles: Control the digestive system and other internal organs.
    - Skeletal muscles/Striated muscles: Responsible for body movement in relation to the environment.
    - Cardiac muscles: Heart muscles that exhibit properties of both skeletal and smooth muscles.

Muscle Fibers

• Muscles consist of individual fibers:
    - Each muscle fiber receives input from only one axon, but a single axon can innervate multiple muscle fibers.
    - Neuromuscular junction: A synapse between a motor neuron axon and a muscle fiber.
    - The release of acetylcholine at this junction prompts muscle contraction.

Antagonistic Muscles

• Movement necessitates alternating contractions of opposing sets of muscles known as antagonistic muscles:
    - Flexor muscles contract to flex or raise an appendage.
    - Extensor muscles contract to extend or straighten an appendage.

Fast and Slow Muscles

• Skeletal muscle types include:
    - Fast-twitch fibers: Enable fast contractions but fatigue quickly.
    - Slow-twitch fibers: Produce less vigorous contractions that resist fatigue.
    - Individuals have various compositions of fast-twitch and slow-twitch muscles.
    - Slow-twitch fibers are aerobic, utilizing oxygen and are ideal for non-strenuous activities, while fast-twitch fibers are anaerobic, leading to fatigue and supporting quick movements.

Temperature and Movement

• The effects of temperature on muscle performance and activity levels are discussed but details are not specified in this segment.

Muscle Control by Proprioceptors

• Proprioceptors: Receptors detecting body part position or movement. Examples include:
    - Muscle spindles: Proprioceptors aligned parallel to the muscle that respond to stretch and initiate muscle contractions through a stretch reflex when tension and stretch are detected.
    - Golgi tendon organs: Located in tendon regions, respond to muscle tension; they inhibit overly vigorous contractions and send impulses to motor neurons.

The Knee-Jerk Reflex

• A common involuntary reflex demonstrated, although details are not explicitly provided.

Voluntary and Involuntary Movements

• Reflexes are involuntary, consistent, automatic responses to stimuli and the majority of movements exhibit a combination of both voluntary and involuntary action.

• Feedback plays a role in movement types; some are ballistic and can't be altered post-initiation, while others are guided by feedback mechanisms.

Sequences of Behaviors

• Behaviors can consist of rapid sequences of individual movements controlled by central pattern generators, which can produce rhythmic motor outputs like bird wing flapping and the “wet dog shake.”

• A motor program represents a learned or instinctive fixed sequence of movements once underway, its execution becomes automatic, interfering with conscious thought. Examples include self-grooming in mice and yawning.

7.2 Brain Mechanisms of Movement

• Insight into brain movement control mechanisms provides potential treatment avenues for spinal cord injuries or limb amputations.

The Cerebral Cortex

• Located in the precentral gyrus of the frontal lobe, the primary motor cortex employs axons connecting to the brainstem and spinal cord for muscle control.

• The cortex is also implicated in more complex movement coordination.

Muscle Control from the Primary Motor Cortex

• The primary motor cortex interacts with various brain areas, such as the premotor cortex, basal ganglia, and others to maintain and execute motor function.

Planning a Movement

• Different areas of the primary motor cortex govern the control of opposing body sides, while overlap exists. Activation of this region occurs upon the intention for movement, thus engaging preparatory mechanisms.

• The posterior parietal cortex is essential in maintaining the body's spatial relationship with the surrounding world, with potential damage leading to impaired coordination of visual stimuli with movement.

Other Areas for Planning a Movement

• Premotor Cortex: Involved in movement preparation, position, posture, and directional organization in spatial contexts.

• Supplementary Motor Cortex: Coordinates rapid sequences in specific orders with inhibition where necessary, active before and after movements.

• Prefrontal Cortex: Functions during delays before movement, storing sensory movement-related information and weighing probable outcomes.

Inhibition of Movements

• The antisaccade task requires inhibition of planned voluntary eye movements towards stimuli, demonstrating necessary prefrontal cortex and basal ganglia engagement that matures through adolescence.

Mirror Neurons

• These neurons fire during movement preparation and while observing similar movement in others, potentially underpinning empathy, understanding, and imitation of behaviors.

Connections from the Brain to the Spinal Cord

• Corticospinal tracts relay signals from the cerebral cortex to regulate muscle control, inclusive of the lateral corticospinal tract and medial corticospinal tract.

Lateral Corticospinal Tract

• Comprised of axons associated with the primary motor cortex, influencing peripheral movements mainly for limbs, and crossing paths at the spinal cord.

Medial Corticospinal Tract

• Composed of axons from various cortical areas, engaging neck, shoulder, and trunk muscles, essential for bilateral movements like walking and bending.

Disorders of the Spinal Cord

• Disorder: Paralysis
    - Description: Inability for voluntary movement
    - Cause: Damage to motor neurons/axons in the spinal cord

• Disorder: Paraplegia
    - Description: Loss of sensation/control in legs
    - Cause: Spinal cord cut in thoracic region

• Disorder: Quadriplegia (Lower Quadriplegia)
    - Description: Loss of sensation/control in both arms and legs
    - Cause: Spinal cord cut in cervical region

• Disorder: Hemiplegia
    - Description: Loss of sensation/control in arm/leg on one side
    - Cause: Damage to one hemisphere of the cerebral cortex

• Disorder: Tabes dorsalis
    - Description: Impaired sensations and control in legs/pelvic area
    - Cause: Damage to dorsal roots from syphilis

• Disorder: Poliomyelitis
    - Description: Paralysis due to virus damaging spinal cord motor neurons

• Disorder: Amyotrophic lateral sclerosis
    - Description: Gradual weakness and paralysis beginning in arms and spreading
    - Cause: Unknown, possibly genetic or toxin exposure.

The Cerebellum

• A brain structure associated with balance and coordination, containing more neurons than any other area.

• Damage results in challenges with rapid movements requiring timing and precision.

The Cerebellum and Functions Other Than Movements

• Responds to sensory information even without movement and reacts to surprising sensory discrepancies, being key in attention mechanisms.

Cellular Organization of the Cerebellum

• Input sources include the spinal cord and sensory systems channeling to the cerebellar cortex, organized in geometrical patterns to refine motor function output.

The Basal Ganglia

• A set of large subcortical structures essential for initiating actions that aren't stimulus-driven, including the caudate nucleus, putamen, and globus pallidus.

Brain Areas and Motor Learning

• Learning new skills involves multiple brain regions, where the basal ganglia play a standout role in mastering motor skills and behavioral patterns.

Conscious Decisions and Movement

• A distinction exists between conscious movement decisions and the action itself, with readiness potentials indicating motor cortex activity prior to voluntary movements, starting at least 200 ms ahead of action execution.

7.3 Movement Disorders

• Disorders like Parkinson’s and Huntington’s disease affect not just movement but influence mood, memory, and cognitive functions.

Parkinson’s Disease

• A disorder marked by tremors, rigidity, and difficulties in movement initiation, impacting cognitive functions and emotional well-being due to dopamine system degeneration.

Immediate Cause of Parkinson’s Disease

• Results from the progressive loss of neurons in the substantia nigra, reducing dopamine supply which slows movement initiation.

Causes of Parkinson’s Disease

• Early-onset variation appears genetically influenced, while late-onset relates to environmental toxin exposure and others. Lifestyle factors like smoking may mitigate risks.

Treatment of Parkinson’s Disease

• L-DOPA: A primary treatment that acts as a dopamine precursor, effective initially but less so over time and intersected with side effects.

Other Possible Treatments for Parkinson’s Disease

• Alternative strategies include receptor-stimulating drugs, deep brain stimulation electrodes, and experimental methods like stem cell implantation.

Huntington’s Disease

• A genetic disorder causing motor symptoms and cognitive decline, typically emerging between ages 30-50, stemming from brain damage in the basal ganglia.

Heredity and Presymptomatic Testing

• Genetic testing can identify risks of Huntington’s with certainty, tied to the C-A-G repeat pattern on chromosome #4, influencing onset timing.

C-A-G Repeats and Huntington’s Disease

• The link between the number of C-A-G repeats and associated neurological disorders suggests a genetic foundation impacting disease severity.